Abstract
2014–2017 was an unprecedented period of successive record-breaking hot years, which coincided with the most severe, widespread, and longest-lasting global-scale coral bleaching event ever recorded. The 2014–2017 global-scale coral bleaching event (GCBE) resulted in very high coral mortality on many reefs, rapid deterioration of reef structures, and far-reaching environmental impacts. Through the papers in this special issue of Coral Reefs entitled The 2014–2017 Global Coral Bleaching Event: Drivers, Impacts, and Lessons Learned, as well as papers published elsewhere, we have a good analysis of the 2014–2017 GCBE and its impacts. These studies have provided key insights into how climate change-driven marine heatwaves are destroying coral reef ecosystems: (a) The 2014–2017 GCBE is unique in the satellite record in its spatial scale, duration, intensity, and repetition of bleaching. (b) The impacts have been the most severe ever seen at many reefs. (c) Timing of observations matters and needs to be considered during the analysis of impacts. (d) On both global and local scales, the intensity of heat stress and impacts varied. (e) We continue to see important differences among and within coral taxa, with key roles played by algal symbionts and the microbiome. (f) Heat stress and bleaching both play a role in subsequent disease, which plays a key role in mortality. (g) Impacts ripple far beyond corals, with significant changes to the fish and invertebrate community that may last decades. (h) The structure of both individual coral’s skeletons and entire reefs has been eroded much more quickly than previously realized. (i) The 2014–2017 GCBE provided little support for the proposed “lifeboat” hypothesis, whereby deep or mesophotic reefs serve as a means of coral reef salvation. (j) While marine protected areas (MPAs) provide protection from local stressors, they not only do not protect reefs from global-scale stressors, but also here is also little evidence they provide significant resilience.
Highlights
Widespread coral bleaching was first witnessed in 1983 as part of the extremely strong 1982–1983 El Nino (Coffroth et al 1990)
Through the papers in this special issue of Coral Reefs entitled The 2014–2017 Global Coral Bleaching Event: Drivers, Impacts, and Lessons Learned, as well as papers published elsewhere, we have a good analysis of the 2014–2017 global-scale coral bleaching event (GCBE) and its impacts
These studies have provided key insights into how climate change-driven marine heatwaves are destroying coral reef ecosystems: (a) The 2014–2017 GCBE is unique in the satellite record in its spatial scale, duration, intensity, and repetition of bleaching. (b) The impacts have been the most severe ever seen at many reefs. (c) Timing of observations matters and needs to be considered during the analysis of impacts
Summary
Widespread coral bleaching was first witnessed in 1983 as part of the extremely strong 1982–1983 El Nino (Coffroth et al 1990). A surprise was the second area of warming off southern Australia in 2016, resulting in bleaching as high as 34°S in Sydney Harbour (Goyen et al 2019) At regional scales, these studies found damage largely followed the degree of heat stress recorded. Severe bleaching and mortality caused declines in the net carbonate production on reefs by reducing carbonate production and increasing erosion (Couch et al 2017; Lange and Perry 2019) Such erosion can be much more rapid than previously understood, as endolithic cyanobacteria can rapidly grow, perforating and weakening the outer part a coral’s skeleton within days to weeks after mortality. This can rapidly flatten the fine structure of colonies, weaken branches (Leggat et al 2019), and significantly reduce rugosity/topographic complexity, within less than a year after bleaching (Couch et al 2017)
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